PO171,2001 F150, 5.4, 4X4, 245,000 mi. Rough idle when warmed up Checked for; vacuum leaks, gas cap, new air/fuel filter, misfire on all 8 cyl, catalytic converter, cleaned MAF with CRC for MAF, cleaned throttle body with B-12.

SOURCE: 2000 Camry 4 cyl 2.2L.

sounds like you have a problem with the spark the coil may be on its way out or there may be oil in the spark plug holls shorting out the spark.
your best bet is to pull the leads out 1 at a time and and look down and check for oil if there is oil there get a new rocker cover gasket.
if no oil refit plug leads loosely and start the car remove one lead at a time slowly and look at the spark cumming out the end off the lead is it blue? if so it is ok if it is yellow and dull you have a coil problem. also check that the spark is only coming out the end of the lead as it may be coming out the side of the lead and shorting to earth,
you can do this by slowly moving the lead around the top of the spark plug holl and see were the spark is coming from

be carfull no to shock your self as it hearts like hell

good luck

SOURCE: car is stalling and idleing irradically.

I Would Suggest That You Complete A Engine Cylinder Leak Down Test.....(not A Compression Test But A Leak Down Test) this will tell you if you have internal problems....possible worn rings or a burnt valve(s) I would use a smoke machine to check for vacuum leaks also. Good Luck

SOURCE: misfiring

See what cylinder is loosing (if that's it) spark. Use a spark tester if you can, or remove plugs and turn it over with the wires on all of the plugs, grounded!

SOURCE: truck has no power.but idles just fine

caylatic converter is probably clogged.

SOURCE: 2003 GMC Sierra Has recently developed

You never replace anything, on a Wishing,Hoping,Pushing,Poking,diagnostic approach

You learn the vehicles Systems,Test,then Replace,if you have a failed component.

Work on the Misfire Issues.
Then you lean O2 Codes will go away.

Not a the plugs.

Think lean---Vacuum leaks,EGR Valve leak,EVAP System leaks,anything with a hose that lets air into the intake system.
Exhaust System leaks,near sensors